This invention relates generally to media handling for inkjet printing systems.
An inkjet printing mechanism is a type of non-impact printing device which forms characters, symbols, graphics or other images by controllably spraying drops of ink. The mechanism typically includes a cartridge, often called a xe2x80x9cpen,xe2x80x9d which houses a printhead. There are various forms of inkjet printheads, known to those skilled in the art, including, for example, thermal inkjet printheads and piezoelectric printheads. The printhead has very small nozzles through which the ink drops are ejected. To print an image the pen is propelled back and forth across a media sheet, while the ink drops are ejected from the printhead in a controlled pattern. Other inkjet printing mechanisms employ a stationary printhead which spans the entire print-zone, and hence are known as a page-wide-array printhead or a print bar. Inkjet printing mechanisms may be employed in a variety of printing systems, such as printers, plotters, scanners, facsimile machines, copiers, and the like.
Typically inkjet printing systems include a roller for feeding a media sheet along a media path. One challenge arising from curling the media sheet around the roller is that the lead or trailing edges of the media sheet may retain some of the curl. As a result the media sheet may curl within the print-zone. Such curling may adversely affect print quality. It is particularly undesirable for the media sheet to curl into contact with the printhead where can damage occur to the media, the printed image, the printhead or the print system. One solution is to increase the spacing between the pen and the media to reduce the likelihood of printhead contact. However, with a varying xe2x80x9cpen to paperxe2x80x9d spacing (xe2x80x9cPPSxe2x80x9d) along the media sheet, print quality is reduced. It is preferred that xe2x80x9cpen to paperxe2x80x9d spacing remain constant along the various portions of the media sheet passing through the print-zone.
An inkjet printing apparatus which moves print media along a media path, includes an inkjet printhead, a drive shaft, pinch devices, and first and second guides. The inkjet printhead has a plurality of inkjet nozzles which eject ink onto a portion of the media located within a print-zone. The drive shaft is located upstream of the printhead and is incrementally rotated to advance the media. The drive shaft has a longitudinal axis, a first radius over a central length and a second radius less than the first radius at a first recess and a second recess, each said recess being peripheral to the central length. A plurality of pinch devices stabilize the media against the drive shaft. The first guide is aligned with the first recess and is spaced from an axis of the drive shaft by a first distance which is less than the first radius. The second guide is aligned with the second recess and is spaced from the axis by a second distance less than the first radius.